Clematis

Clematis wilt is the one dramatic failure of this plant, and it looks far worse than it is. A shoot - or the whole top of a young vine - collapses within a day or two, usually in late spring or early summer just as the flower buds are about to open: leaves and stems go limp, then black and papery, while the roots stay perfectly healthy underground. The cause is a fungus, Calophoma clematidina, which enters through a wound or a leaf node low on a stem and blocks the water-conducting tissue above it. It hits the large-flowered hybrids hardest, especially young plants in their first few years; the small-flowered species and the viticella and texensis groups are largely unaffected. It is rarely fatal to a plant that was planted deeply, because clematis regenerate from dormant buds below the soil line - which is precisely why the deep-planting rule exists.

Watch for: A shoot wilting suddenly from the tip downward over a day or two, the leaves going limp and then black and papery - most often in May or June with the buds still unopened. A dark, sunken, sometimes split patch on the stem low down, often at a leaf node, with everything above it dead and everything below it still green. Whole young plants collapsing while the soil is moist and the roots, if you scrape down, are firm and pale. Damage restricted to a large-flowered hybrid while a viticella or a species clematis a few feet away is untouched. Leaf stalks blackening where they join the stem, which is often the earliest visible sign.

Prevent: Plant deep - this is the defense that actually works. Set the crown 2 to 4 inches BELOW the soil surface, deeper than it sat in the pot, so there are dormant buds underground that can rebuild the plant if the top is lost. Buy a strong plant with several stems rather than a single whip, and cut a new plant back to about 12 inches its first late winter to build a multi-stemmed base. Protect the brittle lower stems from injury, since wounds are the entry point: a collar of wire mesh, a length of pipe, or a low shrub at the base keeps string trimmers and hoes away. Tie stems in gently and often, because a snapped stem is an open door. Keep the roots cool and evenly moist, water at the base rather than overhead, and clear fallen clematis foliage in autumn. Where wilt has been a recurring problem, plant a viticella, texensis or small-flowered species instead - they are effectively resistant.

Treat: Cut the affected stem right out, back below the dark lesion into clean healthy tissue, or to ground level if the whole stem has gone, and bin the material rather than composting it. Sterilize the pruners afterward so you are not carrying it to the next plant. Then water, mulch and wait: a deeply planted clematis usually pushes new shoots from below the soil line within a few weeks, and often flowers again later the same season. Do not dig the plant up in the first year after a collapse - the roots are alive, and this is exactly the situation deep planting was for. Fungicides are not a practical home control and cannot reach a fungus already inside the stem. If a plant wilts repeatedly over several seasons, replace it with a viticella or species clematis in fresh soil rather than persisting with the same hybrid in the same spot.

Overwhelmingly a large-flowered-hybrid problem, and overwhelmingly a young-plant problem. If you have lost one clematis to wilt, the two changes that matter are planting the next one deep and choosing a viticella.

Slugs and snails are nocturnal mollusks that rasp ragged holes in soft leaves, shear off seedlings at ground level, and chew into ripe fruit that touches the soil. They feed at night and in the early morning and spend the day hidden under boards, pots, dense mulch, leaf litter, and low foliage, becoming active in exactly the cool, damp, shaded conditions that suit young plants. Damage is heaviest in wet spells and on tender spring growth: a single wet week can erase a row of seedlings while an established, tough-leaved plant of the same species is barely marked. They lay clusters of small pearly eggs in damp soil and under debris, so a garden with plenty of cover carries a resident population year after year rather than being invaded from outside.

Watch for: Irregular ragged holes chewed out of the middle of leaves and along the edges - not the clean-edged cuts a caterpillar leaves. Seedlings that vanish overnight, or that are cut off at soil level with nothing left behind. Silvery dried slime trails across leaves, soil, pots, and paving in the morning: this is the giveaway that tells you it was mollusks rather than an insect. Chewed pits in ripe fruit, especially where it rests on the ground. Damage that shows up on the lowest, dampest leaves first and gets worse after rain or evening watering. Turn over a board, an upturned pot, or a clump of dense mulch during the day and look for the animals themselves sheltering in the cool underneath.

Prevent: Take away the daytime shelter first: lift boards and upturned pots, clear piles of debris, keep dense mulch pulled back from crowns and stems, and give crowded plantings enough airflow to dry out. Water in the morning rather than the evening so the surface is dry by the time they come out. Copper tape around containers and raised beds gives them a shock they will not cross, and it is the one barrier that reliably works. Get plants past the vulnerable stage quickly - start seedlings in pots and set them out at a decent size rather than direct-sowing into a cold wet bed, since most plants stop being worth defending once the leaves toughen. Leave the ground beetles, frogs, toads, and ground-feeding birds alone, because they eat mollusks all night for free and broad-spectrum slug pellets kill them too. Where thick-leaved or resistant varieties exist for what you are growing, they take far less damage.

Treat: Hand-picking works and costs nothing: go out an hour after dark with a headlamp, drop what you find into soapy water, and repeat nightly for a week or two - persistence is what wins, not any single product. Shallow beer traps sunk to soil level catch them too, but need emptying and refilling daily to be worth anything. Iron-phosphate bait is the standard control and is far lower-risk around pets and wildlife than the old metaldehyde products, but it is not harmless: many formulations include EDTA, and a dog that eats a quantity of pellets can develop iron toxicosis. Scatter it thinly per the label, never in piles, and keep dogs off a baited bed. Clear fallen foliage and debris in autumn, where the eggs are laid. In a wet climate this is a population you manage each season rather than one you eradicate - and on most established plants light grazing is cosmetic and needs nothing at all.

The hidden cost of hard pruning: a Group 3 clematis cut to 12 inches sends its entire season up from ground level in spring, and slugs shear those first soft shoots off overnight. Losing them can cost the year's flowers. Protect the crown from the moment growth starts until the shoots are a foot tall and toughening - pull the mulch back off the crown, and hand-pick after dark for the two or three weeks that matter.

A direct hazard to people, pets and livestock, shared across the genus. Clematis, like other members of the buttercup family, contains ranunculin, which converts on crushing or chewing to protoanemonin - an acrid irritant. Contact with the sap causes stinging, redness and, in sensitive people, genuine blistering after prolonged handling, and chewing any part burns the mouth and causes drooling, vomiting and diarrhea. Drying breaks the compound down, so dried plant material is not the concern; fresh growth is.

Watch for: Itching, redness or blisters on hands and forearms after an afternoon of cutting or pulling; drooling, mouth pawing or vomiting in a pet that has chewed the vine; grazing animals with access to fresh growth along a fence line.

Prevent: Wear gloves and long sleeves for any cutting, pulling or pruning, and wash skin afterward. Keep fresh growth away from chewing pets and grazing animals, and do not leave fresh cuttings where livestock can reach them.

Treat: For skin contact, wash the area promptly with soap and water and treat as contact dermatitis; see a clinician for extensive blistering. If a person or pet has chewed or swallowed any part, rinse the mouth and call poison control or your veterinarian rather than waiting for symptoms.

The exposure that catches gardeners out is the annual Group 3 cut-down, which means handling armfuls of fresh stems and leaves in one session. Gloves and long sleeves for that job specifically, and wash afterward. Garden clematis is not a plant to keep where a dog or a goat chews the fence line.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Colonies build on the soft spring shoot tips and on the flower buds, and they collapse under predators by early summer on an established plant. Aim a hose jet carefully - clematis stems snap easily - and watch a hard-pruned Group 3 vine in particular, which is nothing but soft new tissue in May.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.

Watch for: Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Prevent: Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Treat: Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

Mostly a late-summer disfigurement of the large-flowered hybrids, worst on a plant crowded against a still, shaded wall or tucked under a house eave where rain never reaches it. The viticella group is rarely troubled. Airflow does more than spraying: mount the support clear of the wall, thin congested growth, and water at the base. On a Group 3 plant it is largely moot, since the whole vine comes off in late winter anyway.